Virus linked to bee colony deaths

Other factors involved, say researchers

Other factors involved, say researchers

September 07, 2007|By Thomas H. Maugh II, Los Angeles Times

Scientists have found a virus that is associated with the destruction of a large fraction of American commercial bee colonies, but they have not been able to prove that it is the cause of the mysterious disease that has wreaked havoc on the bee industry. The virus, called Israeli acute paralysis, may have been brought into the United States in bees imported from Australia. That importation was first permitted in 2004, about the same time that the new disease - called Colony Collapse Disorder, or CCD - began appearing in the U.S. Australian bees do not suffer from CCD, leading researchers to speculate that the virus acts synergistically with chemicals in the environment or with another infectious agent, such as the varroa mite, which is not common in Australia. More testing: Experiments are under way to determine which combination of virus and chemical or infectious agent, if any, causes the disease, and researchers hope to have an answer this year. Researchers also are examining archived bee specimens to determine whether the virus was present before 2004. “Our results indicate that (the virus) is a significant marker for CCD,” said Dr. W. Ian Lipkin of Columbia University's Mailman School of Public Health, a co-author of the report published online Thursday by the journal Science. “The next step is to ascertain whether (the virus), alone or in concert with other factors, can induce CCD in healthy bees.” But researchers from the U.S. Army's Edgewood Chemical Biological Center in Maryland cautioned that they had unpublished results in which they found the Israeli virus in non-CCD colonies. Although America has had many bee die-offs in the past, the latest episode has been one of the worst, affecting an estimated 23 percent of beekeepers. Typically, from 50 percent to 90 percent of a keeper's colonies are affected, with the worker bees simply failing to return to their hives, leaving behind the queen and a handful of newborn bees. Agricultural experts have viewed the deaths with alarm because bees are required to pollinate about a third of the nation's food crops, including almonds, cherries, blueberries, pears, strawberries and pumpkins. The number of bee colonies in the country is about 2.5 million, down from 5 million in the 1940s and 1950s. New findings: In May, scientists from around the country formed a working group led by Cox-Foster and entomologist Jeffery S. Pettis of the U.S. Department of Agriculture to track down the cause of the deaths. They enlisted virologist Lipkin to look for pathogens infecting the sick bees, using samples from four sick colonies around the United States and healthy colonies from Hawaii and Pennsylvania. Lipkin and his colleagues ground up the bees, extracted RNA, sequenced it and matched the non-honeybee sequences to known databases. The results surprised everybody. All of the bees had a set of eight distinctive bacteria “that have not been found in any other environment or host,” said co-author Nancy A. Moran of the University of Arizona. “They are all unnamed species about which we know very little. They probably perform essential functions in bees, providing essential nutrients or contributing defenses against pathogens.” Similarly, there was “a remarkably high viral burden in bee populations, both those with CCD and those without it,” said co-author Edward C. Holmes of Penn State University. “There were seven different viruses, but only one was consistently found with CCD.” Research offers hope: Israeli acute paralysis virus was found in all the CCD specimens, but in neither of the healthy specimens. The virus was discovered in 2002 in dead bees from Israeli colonies by virologist Ilan Sela of the University of Jerusalem. In experiments reported this summer, Sela found that injecting the virus into bees killed 98 percent of recipients within days. The symptoms in the Israeli bees - shivering wings, paralysis and death - are different from those exhibited by American bees. But Holmes speculated that the virus might have undergone genetic changes that had altered its pathogenicity. Or it may be that the symptoms are different in bees whose immune systems are stressed by the varroa mite or by being trucked from farm to farm during the growing season. The finding does offer one ray of hope. Sela has reported that about 30 percent of bees he studied in Israel had incorporated the viral genome into their genetic blueprint and had become resistant to the virus. If the virus is shown to be the cause of CCD, it may be possible to replace current bee colonies with hives of resistant specimens.